The present invention relates generally to thermostats used for heating and cooling systems, such as gas or electric forced air furnaces, gas or electric radiant heating furnaces, electric forced air air-conditioning systems, and electric heat pumps. Invention may also be suitable for other types of systems, including solar and solar electric heating and cooling systems.
Digital set-back programmable thermostats typically use a screen, such as a liquid-crystal display (LCD), to display both operational functions and programming values. The user enters commands into the thermostat, such as for setting the current time and date and programming the thermostat, by pressing keys or pressing appropriate positions on a touch screen display. In many cases a set of instructions explaining the steps that must be taken to operate the thermostat is printed on the thermostat or separately documented so that programming such a thermostat can be quite confusing and tedious. Also, programming conventional thermostats is typically accomplished only after selecting a series of different screens on the display. In addition, information relating to the status of the thermostat and the settings in the program controlling the thermostat is often accessible only by reviewing different screens on the display.
Many thermostats are used to control both a furnace in the heating mode and an air-conditioning unit in the cooling mode. The heating and cooling modes are typically controlled manually. That is, the user sets the thermostat to either cool or heat so that only the furnace or only the air-conditioning unit is operational in the chosen mode.
Many programmable thermostats have only heating, off, and cooling modes. Programmable thermostats that have an automatic setting, sometimes referred to as auto thermostats, typically have heating, auto, cooling, and off modes. In both cases, the user can put in separate setting times and temperatures from a heating program and a cooling program. Auto thermostats automatically switch between the user's heating and cooling programs as a function of room temperature.
There are typically two limitations associated with conventional auto thermostats. One limitation is that heating and cooling program times must be the same; that is, the times for each period (typically morning, day, evening, and night) must be the same. The other limitation is that the user's cooling program target temperature can never be closer than X degrees (typically 3° F.) to the user's heating program target temperature. So if the user sets the heating target temperature to 70, the cooling target temperature cannot be set any closer than 73 in this example. When the user tries to lower the cooling target temperature below 73, the programming of the thermostat typically just stops and frustrates the user. Likewise, if the user wants to raise the heat setting, for example changing the heating target temperature from 70 to 72, the higher temperature may be too close to the cooling target temperature so that the programming of the thermostat may also stop.
Although programmable thermostats hold out the promise of reducing the energy used by heating systems, the U.S. Environmental Protection Agency, which provides the ENERGY STAR certification for appliances and other devices, has expressed concern that potential energy savings are not being realized because of the difficulties consumers face trying to program conventional digital thermostats.